1. Field of the Invention
Exemplary embodiments of the present invention relate to a sheet transport mechanism that feeds and conveys a sheet in a predetermined direction and an image forming apparatus incorporating the above-described sheet transport mechanism.
2. Discussion of the Related Art
In some related-art image forming apparatuses, in a sheet transport path along which sheets of recording media are conveyed, the leading edge of any given sheet tends to get snagged or caught at a boundary between adjacent units along the sheet transport path. To avoid this problem, the sheet transport path is typically given a recessed portion or step at the boundary. Specifically, a downstream unit, that is, the unit provided downstream in a sheet transport direction of the sheet transport path, is recessed from the upstream unit, that is, the unit provided upstream in the sheet transport direction of the sheet transport path.
As a further aid to the smooth conveyance of the sheets, for example, at a meeting point where two original sheet transport paths meet, the width of a merged sheet transport path downstream from the meeting point is greater than the widths of each of the two original sheet transport paths upstream from the meeting point. This structure of the sheet transport path can convey a sheet smoothly from the two original sheet transport paths via the meeting point toward the downstream direction from the meeting point.
Positions of units and mechanisms that constitute an image forming apparatus, such as a sheet transport mechanism, an image forming mechanism, a transfer unit, and a fixing unit can be variously arranged depending on the desired functional purposes. Consequently, sheet transport paths may be curved or bent as needed, and therefore a sheet may also be curved or bent when passing through a curved portion of the sheet transport path. However, while traveling in the sheet transport path that is curved or bent, the restorative force of the sheet tends to bring the curved sheet back to its original flat shape. As a result, the trailing edge of the sheet strikes or flaps against a recessed downstream unit or portion when passing the stepped boundary in the sheet transport path, which produces a flapping noise with the trailing edge of the sheet (hereinafter, also referred to as “trailing edge flapping noise”).
As previously noted, if a sheet transport path having the meeting point at which two or more sheet transport paths meet is curved or bent, the width of the merged sheet transport path downstream from the meeting point is greater than the widths of each of the two sheet transport paths upstream from the meeting point. Therefore, the sheet transport path includes the different levels or steps in the vicinity of the meeting point, which can also produce the trailing edge flapping noise.
To eliminate such flapping noise, one approach, for example, involves a unit that includes a seam or bump between adjacent members that constitute the unit that is configured such that a member disposed downstream from the seam includes a portion to lift up the trailing edge of a sheet from the member so as to prevent production of flapping noise. However, this configuration cannot raise the trailing edge of the sheet in space reliably without increasing a relative angle at a sheet entrance path when the leading edge of the sheet enters a downstream guide member therefrom. It is then likely that a sheet transport load from the downstream guide member increases, resulting in a paper jam. In addition, a sheet having greater rigidity can exert a larger restorative force. The foregoing arrangement cannot reduce flapping noise of the rigid sheet.
Another approach involves an image forming apparatus that includes guide members, with a seam formed between the guide members angled in a width direction of the guide members. This structure can cause the trailing edge of a sheet to hit different parts of the seam at different times. Even though this configuration can reduce the occurrence of flapping noise, the flapping noise can still occur. Further, if the sheet transport path is constricted due to a cramped layout design, an angle of the seam sufficient to prevent the flapping noise cannot be obtained.
Yet another approach involves a mechanism that includes a movable guide member at a convergence part that controls the configuration of two curved guide paths. That is, when a sheet enters from one of the sheet entrance paths, the movable guide member is maintained to eliminate a step formed by a first curved guide of the two paths. However, this configuration requires a sequence reflecting method performed by a control unit and a driving member to drive the rotary member are needed, which has large drawbacks and demerits in costs.